syncthing-event-api

title: syncthing-event-api(7)

summary: Event API

text:
# syncthing-event-api(7)

## NAME
syncthing-event-api - Event API

## DESCRIPTION
Syncthing provides a simple long polling interface for exposing events from the core utility towards a GUI. To receive events, see GET /rest/events.

## EVENT STRUCTURE
Each event is represented by an object similar to the following:

```
{

    "id": 2,

    "globalID": 3,

    "type": "DeviceConnected",

    "time": "2014-07-13T21:04:33.687836696+02:00",

    "data": {

        "addr": "172.16.32.25:22000",

        "id": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG"

    }
}
```

The top level keys id, globalID, time, type and data are always present, though data may be null.

id

A unique ID for this event on the events API. It always increases by 1: the first event generated has id 1, the next has id 2 etc. If this increases by more than 1, then one or more events have been skipped by the events API.

globalID

A global ID for this event, across the events API, the audit log, and any other sources. It may increase by more than 1, but it will always be greater than or equal to the id.

time

The time the event was generated.

type

Indicates the type of (i.e. reason for) the event and is one of the event types below.

data

An object containing optional extra information; the exact structure is determined by the event type.

## EVENT TYPES

### ClusterConfigReceived
Added in version 1.20.0.

The ClusterConfigReceived event is emitted after processing such a protocol message received from a remote device. It is mainly used for internal purposes.

```
{

    "id": 84,

    "globalID": 84,

    "type": "ClusterConfigReceived",

    "time": "2022-04-27T14:14:27.043576583+09:00",

    "data": {

        "device": "I6KAH76-66SLLLB-5PFXSOA-UFJCDZC-YAOMLEK-CP2GB32-BV5RQST-3PSROAU"

    }
}
```

### ConfigSaved
Emitted after the config has been saved by the user or by Syncthing itself.

```
{

    "id": 50,

    "globalID": 50,

    "type": "ConfigSaved",

    "time": "2014-12-13T00:09:13.5166486Z",

    "data": {

        "version": 7,

        "folders": [{"..."}],

        "devices": [{"..."}],

        "gui": {"..."},

        "ldap": {"..."},

        "options": {"..."},

        "remoteIgnoredDevices": [{"..."}],

        "defaults": {"..."}

    }
}
```

### DeviceConnected
Generated each time a connection to a device has been established.

```
{

    "id": 2,

    "globalID": 2,

    "type": "DeviceConnected",

    "time": "2014-07-13T21:04:33.687836696+02:00",

    "data": {

        "addr": "172.16.32.25:22000",

        "id": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG",

        "deviceName": "Laptop",

        "clientName": "syncthing",

        "clientVersion": "v0.13.4",

        "type": "TCP (Client)"

    }
}
```

### DeviceDisconnected
Generated each time a connection to a device has been terminated.

```
{

    "id": 48,

    "globalID": 48,

    "type": "DeviceDisconnected",

    "time": "2014-07-13T21:18:52.859929215+02:00",

    "data": {

        "error": "unexpected EOF",

        "id": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG"

    }
}
```

NOTE:

The error key contains the cause for disconnection, which might not necessarily be an error as such. Specifically, “EOF” and “unexpected EOF” both signify TCP connection termination, either due to the other device restarting or going offline or due to a network change.

### DeviceDiscovered
Emitted when a new device is discovered using local discovery.

```
{

    "id": 13,

    "globalID": 13,

    "type": "DeviceDiscovered",

    "time": "2014-07-17T13:28:05.043465207+02:00",

    "data": {

        "addrs": [

            "172.16.32.25:22000"

        ],

        "device": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG"

    }
}
```

### DevicePaused
Emitted when a device was paused.

```
{

    "id": 13,

    "globalID": 13,

    "type": "DevicePaused",

    "time": "2014-07-17T13:28:05.043465207+02:00",

    "data": {

        "device": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG"

    }
}
```

### DeviceRejected (DEPRECATED)
Deprecated since version v1.13.0: This event is still emitted for compatibility, but deprecated. Use the replacement PendingDevicesChanged event instead.

Emitted when there is a connection from a device we are not configured to talk to.

```
{

    "id": 24,

    "globalID": 24,

    "type": "DeviceRejected",

    "time": "2014-08-19T10:43:00.562821045+02:00",

    "data": {

        "address": "127.0.0.1:51807",

        "name": "My dusty computer",

        "device": "EJHMPAQ-OGCVORE-ISB4IS3-SYYVJXF-TKJGLTU-66DIQPF-GJ5D2GX-GQ3OWQK"

    }
}
```

### DeviceResumed
Generated each time a device was resumed.

```
{

    "id": 2,

    "globalID": 2,

    "type": "DeviceResumed",

    "time": "2014-07-13T21:04:33.687836696+02:00",

    "data": {

        "device": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG"

    }
}
```

### DownloadProgress
Emitted during file downloads for each folder for each file. By default only a single file in a folder is handled at the same time, but custom configuration can cause multiple files to be shown.

```
{

    "id": 221,

    "globalID": 221,

    "type": "DownloadProgress",

    "time": "2014-12-13T00:26:12.9876937Z",

    "data": {

        "folder1": {

            "file1": {

                "total": 800,

                "pulling": 2,

                "copiedFromOrigin": 0,

                "reused": 633,

                "copiedFromElsewhere": 0,

                "pulled": 38,

                "bytesTotal": 104792064,

                "bytesDone": 87883776

            },

            "dir\\file2": {

                "total": 80,

                "pulling": 2,

                "copiedFromOrigin": 0,

                "reused": 0,

                "copiedFromElsewhere": 0,

                "pulled": 32,

                "bytesTotal": 10420224,

                "bytesDone": 4128768

            }

        },

        "folder2": {

            "file3": {

                "total": 800,

                "pulling": 2,

                "copiedFromOrigin": 0,

                "reused": 633,

                "copiedFromElsewhere": 0,

                "pulled": 38,

                "bytesTotal": 104792064,

                "bytesDone": 87883776

            },

            "dir\\file4": {

                "total": 80,

                "pulling": 2,

                "copiedFromOrigin": 0,

                "reused": 0,

                "copiedFromElsewhere": 0,

                "pulled": 32,

                "bytesTotal": 10420224,

                "bytesDone": 4128768

            }

        }

    }
}
```

- total - total number of blocks in the file

- pulling - number of blocks currently being downloaded

- copiedFromOrigin - number of blocks copied from the file we are about to replace

- reused - number of blocks reused from a previous temporary file

- copiedFromElsewhere - number of blocks copied from other files or potentially other folders

- pulled - number of blocks actually downloaded so far

- bytesTotal - approximate total file size

- bytesDone - approximate number of bytes already handled (already reused, copied or pulled)

Where block size is 128KB.

Files/folders appearing in the event data imply that the download has been started for that file/folder, where disappearing implies that the downloads have been finished or failed for that file/folder. There is always a last event emitted with no data, which implies all downloads have finished/failed.

### Failure
Generated for specific errors that will also be sent to the usage reporting server, if enabled in the configuration. These are usually of special interest to the developers to troubleshoot complex errors. The data field contains a textual error message.

```
{

  "id": 93,

  "globalID": 93,

  "type": "Failure",

  "time": "2021-06-07T21:22:03.414609034+02:00",

  "data": "index handler got paused while already paused"
}
```

### FolderCompletion
The FolderCompletion event is emitted when the local or remote contents for a folder changes. It contains the completion percentage for a given remote device and is emitted once per currently connected remote device.

Added in version 1.20.0: Indication whether the remote device has accepted the folder (shares it with us) as well, and whether it is paused. The remoteState field is unknown when the remote device is not connected. Otherwise it can be either paused, notSharing, or valid if the remote is sharing back.

```
{

    "id": 84,

    "globalID": 84,

    "type": "FolderCompletion",

    "time": "2022-04-27T14:14:27.043576583+09:00",

    "data": {

        "completion": 100,

        "device": "I6KAH76-66SLLLB-5PFXSOA-UFJCDZC-YAOMLEK-CP2GB32-BV5RQST-3PSROAU",

        "folder": "default",

        "globalBytes": 17,

        "globalItems": 4,

        "needBytes": 0,

        "needDeletes": 0,

        "needItems": 0,

        "remoteState": "valid",

        "sequence": 12

    }
}
```

### FolderErrors
The FolderErrors event is emitted when a folder cannot be successfully synchronized. The event contains the ID of the affected folder and a list of errors for files or directories therein. This list of errors is obsolete once the folder changes state to syncing - if errors remain after the next synchronization attempt, a new FolderErrors event is emitted.

```
{

    "id": 132,

    "type": "FolderErrors",

    "time": "2015-06-26T13:39:24.697401384+02:00",

    "data": {

        "errors": [

            {

                "error": "open /Users/jb/src/github.com/syncthing/syncthing/test/s2/h2j/.syncthing.aslkjd.tmp: permission denied",

                "path": "h2j/aslkjd"

            }

        ],

        "folder": "default"

    }
}
```

Added in version 0.11.12.

SEE ALSO:

The StateChanged event.

### FolderPaused
Generated when the configuration changes regarding the “paused” state of a folder. Sent repeatedly for each changed folder.

```
{

  "id": 93,

  "globalID": 93,

  "type": "FolderPaused",

  "time": "2021-06-07T23:45:03.414609034+02:00",

  "data": {

    "id": "abcde-fghij",

    "label": "My folder"

  }
}
```

### FolderRejected (DEPRECATED)
Deprecated since version v1.13.0: This event is still emitted for compatibility, but deprecated. Use the replacement PendingFoldersChanged event instead.

Emitted when a device sends index information for a folder we do not have, or have but do not share with the device in question.

```
{

    "id": 27,

    "globalID": 27,

    "type": "FolderRejected",

    "time": "2014-08-19T10:41:06.761751399+02:00",

    "data": {

        "device": "EJHMPAQ-OGCVORE-ISB4IS3-SYYVJXF-TKJGLTU-66DIQPF-GJ5D2GX-GQ3OWQK",

        "folder": "GXWxf-3zgnU",

        "folderLabel": "My Pictures"

    }
}
```

### FolderResumed
Generated when the configuration changes regarding the “paused” state of a folder. Sent repeatedly for each changed folder.

```
{

  "id": 93,

  "globalID": 93,

  "type": "FolderResumed",

  "time": "2021-06-07T23:45:03.414609034+02:00",

  "data": {

    "id": "abcde-fghij",

    "label": "My folder"

  }
}
```

### FolderScanProgress
Emitted in regular intervals (folder setting ProgressIntervalS, 2s by default) during scans giving the amount of bytes already scanned and to be scanned in total , as well as the current scanning rates in bytes per second.

```
{

   "data" : {

      "total" : 1,

      "rate" : 0,

      "current" : 0,

      "folder" : "bd7q3-zskm5"

   },

   "globalID" : 29,

   "type" : "FolderScanProgress",

   "time" : "2017-03-06T15:00:58.072004209+01:00",

   "id" : 29
}
```

### FolderSummary
The FolderSummary event is emitted when folder contents have changed locally. This can be used to calculate the current local completion state.

```
{

    "id": 16,

    "type": "FolderSummary",

    "time": "2024-01-31T08:27:30.777875+01:00",

    "data": {

        "folder": "default",

        "summary": {

            "error": "",

            "errors": 0,

            "globalBytes": 4,

            "globalDeleted": 18664,

            "globalDirectories": 0,

            "globalFiles": 1,

            "globalSymlinks": 0,

            "globalTotalItems": 18665,

            "ignorePatterns": false,

            "inSyncBytes": 4,

            "inSyncFiles": 1,

            "invalid": "",

            "localBytes": 4,

            "localDeleted": 18664,

            "localDirectories": 0,

            "localFiles": 1,

            "localSymlinks": 0,

            "localTotalItems": 18665,

            "needBytes": 0,

            "needDeletes": 0,

            "needDirectories": 0,

            "needFiles": 0,

            "needSymlinks": 0,

            "needTotalItems": 0,

            "pullErrors": 0,

            "receiveOnlyChangedBytes": 0,

            "receiveOnlyChangedDeletes": 0,

            "receiveOnlyChangedDirectories": 0,

            "receiveOnlyChangedFiles": 0,

            "receiveOnlyChangedSymlinks": 0,

            "receiveOnlyTotalItems": 0,

            "remoteSequence": {

                "MRIW7OK-NETT3M4-N6SBWME-N25O76W-YJKVXPH-FUMQJ3S-P57B74J-GBITBAC": 37329

            },

            "sequence": 37329,

            "state": "idle",

            "stateChanged": "2024-01-31T08:27:24+01:00",

            "version": 37329,

            "watchError": ""

        }

    }
}
```

### FolderWatchStateChanged
The FolderWatchStateChanged event is emitted when a folder’s watcher routine encounters a new error, or when a previous error disappeared after retrying. The event contains the ID of the affected folder and textual error messages describing the previous (from) and the updated (to) error conditions. If there was no error in either of these, the respective field is omitted.

```
{

  "id": 123,

  "type": "FolderWatchStateChanged",

  "time": "2022-03-14T12:34:56.890000000+01:00",

  "data": {

    "folder": "default",

    "from": "Something bad happened.",

    "to": "Something worse happened."

  }
}
```

### ItemFinished
Generated when Syncthing ends synchronizing a file to a newer version. A successful operation:

```
{

    "id": 93,

    "globalID": 93,

    "type": "ItemFinished",

    "time": "2014-07-13T21:22:03.414609034+02:00",

    "data": {

        "item": "test.txt",

        "folder": "default",

        "error": null,

        "type": "file",

        "action": "update"

    }
}
```

An unsuccessful operation:

```
{

    "id": 44,

    "globalID": 44,

    "type": "ItemFinished",

    "time": "2015-05-27T11:21:05.711133004+02:00",

    "data": {

        "action": "update",

        "error": "open /Users/jb/src/github.com/syncthing/syncthing/test/s2/foo/.syncthing.hej.tmp: permission denied",

        "folder": "default",

        "item": "foo/hej",

        "type": "file"

    }
}
```

The action field is either update (contents changed), metadata (file metadata changed but not contents), or delete.

Added in version 0.11.10: The metadata action.

### ItemStarted
Generated when Syncthing begins synchronizing a file to a newer version.

```
{

    "id": 93,

    "globalID": 93,

    "type": "ItemStarted",

    "time": "2014-07-13T21:22:03.414609034+02:00",

    "data": {

        "item": "test.txt",

        "folder": "default",

        "type": "file",

        "action": "update"

    }
}
```

The action field is either update (contents changed), metadata (file metadata changed but not contents), or delete.

Added in version 0.11.10: The metadata action.

### ListenAddressesChanged
This event is emitted when a listen address changes.

```
{

   "type" : "ListenAddressesChanged",

   "id" : 70,

   "time" : "2017-03-06T15:01:24.88340663+01:00",

   "globalID" : 70,

   "data" : {

      "address" : {

         "Fragment" : "",

         "RawQuery" : "",

         "Scheme" : "dynamic+https",

         "Path" : "/endpoint",

         "RawPath" : "",

         "User" : null,

         "ForceQuery" : false,

         "Host" : "relays.syncthing.net",

         "Opaque" : ""

      },

      "wan" : [

         {

            "ForceQuery" : false,

            "User" : null,

            "Host" : "31.15.66.212:443",

            "Opaque" : "",

            "Path" : "/",

            "RawPath" : "",

            "RawQuery" : "id=F4HSJVO-CP2C3IL-YLQYLSU-XTYODAG-PPU4LGV-PH3MU4N-G6K56DV-IPN47A&pingInterval=1m0s&networkTimeout=2m0s&sessionLimitBps=0&globalLimitBps=0&statusAddr=:22070&providedBy=",

            "Scheme" : "relay",

            "Fragment" : ""

         }

      ],

      "lan" : [

         {

            "RawQuery" : "id=F4HSJVO-CP2C3IL-YLQYLSU-XTYODAG-PPU4LGV-PH3MU4N-G6K56DV-IPN47A&pingInterval=1m0s&networkTimeout=2m0s&sessionLimitBps=0&globalLimitBps=0&statusAddr=:22070&providedBy=",

            "Scheme" : "relay",

            "Fragment" : "",

            "RawPath" : "",

            "Path" : "/",

            "Host" : "31.15.66.212:443",

            "Opaque" : "",

            "ForceQuery" : false,

            "User" : null

         }

      ]

   }
}
```

### LocalChangeDetected
Generated upon scan whenever the local disk has discovered an updated file from the previous scan. This does not include events that are discovered and copied from other devices (RemoteChangeDetected), only files that were changed on the local filesystem.

NOTE:

This event is not included in GET /rest/events endpoint without a mask specified, but needs to be selected explicitly.

```
{

  "id": 7,

  "globalID": 59,

  "time": "2016-09-26T22:07:10.7189141-04:00",

  "type": "LocalChangeDetected",

  "data": {

    "action": "deleted",

    "folder": "vitwy-zjxqt",

    "folderID": "vitwy-zjxqt",

    "label": "TestSync",

    "path": "test file.rtf",

    "type": "file"

  }
}
```

Deprecated since version v1.1.2: The folderID field is a legacy name kept only for compatibility. Use the folder field with identical content instead.

### LocalIndexUpdated
Generated when the local index information has changed, due to synchronizing one or more items from the cluster or discovering local changes during a scan.

```
{

    "id": 59,

    "globalID": 59,

    "type": "LocalIndexUpdated",

    "time": "2014-07-17T13:27:28.051369434+02:00",

    "data": {

        "folder": "default",

        "items": 1000,

        "filenames": [

            "foo",

            "bar",

            "baz"

        ],

        "sequence": 12345,

        "version": 12345

    }
}
```

Deprecated since version v1.10.0: The version field is a legacy name kept only for compatibility. Use the sequence field with identical content instead.

### LoginAttempt
When authentication is enabled for the GUI, this event is emitted on every login attempt. If either the username or password are incorrect, success is false and in any case the given username is returned.

```
{

   "id" : 187,

   "time" : "2017-03-07T00:19:24.420386143+01:00",

   "data" : {

      "remoteAddress" : "127.0.0.1",

      "username" : "somename",

      "success" : false

   },

   "type" : "LoginAttempt",

   "globalID" : 195
}
```

If the X-Forwared-For header is present and the connecting host is either on localhost or on the same LAN, it will be treated as a reverse proxy. In this case, the remoteAddress field is filled with the leftmost IP address from the header, and the additional proxy field retains the original IP of the connecting host.

```
{

   "id" : 187,

   "time" : "2017-03-07T00:19:24.420386143+01:00",

   "data" : {

      "proxy" : "127.0.0.1",

      "remoteAddress" : "192.168.178.10",

      "username" : "somename",

      "success" : false

   },

   "type" : "LoginAttempt",

   "globalID" : 195
}
```

### PendingDevicesChanged
Added in version 1.14.0.

Emitted when pending devices were added / updated (connection from unknown ID) or removed (device is ignored, dismissed or added).

```
{

  "id": 87,

  "type": "PendingDevicesChanged",

  "time": "2020-12-22T22:24:37.578586718+01:00",

  "data": {

    "added": [

      {

        "address": "127.0.0.1:51807",

        "deviceID": "EJHMPAQ-OGCVORE-ISB4IS3-SYYVJXF-TKJGLTU-66DIQPF-GJ5D2GX-GQ3OWQK",

        "name": "My dusty computer"

      }

    ],

    "removed": [

      {

        "deviceID": "P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"

      }

    ]

  }
}
```

### PendingFoldersChanged
Added in version 1.14.0.

Emitted when pending folders were added / updated (offered by some device, but not shared to them) or removed (folder ignored, dismissed or added or no longer offered from the remote device). A removed entry without a deviceID attribute means that the folder is no longer pending for any device.

```
{

  "id": 101,

  "type": "PendingFoldersChanged",

  "time": "2020-12-22T22:36:55.66744317+01:00",

  "data": {

    "added": [

      {

        "deviceID": "EJHMPAQ-OGCVORE-ISB4IS3-SYYVJXF-TKJGLTU-66DIQPF-GJ5D2GX-GQ3OWQK",

        "folderID": "GXWxf-3zgnU",

        "folderLabel": "My Pictures"

        "receiveEncrypted": "false"

        "remoteEncrypted": "false"

      }

    ],

    "removed": [

      {

        "deviceID": "P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2",

        "folderID": "neyfh-sa2nu"

      },

      {

        "folderID": "abcde-fghij"

      }

    ]

  }
}
```

### RemoteChangeDetected
Generated upon scan whenever a file is locally updated due to a remote change. Files that are updated locally produce a LocalChangeDetected event.

NOTE:

This event is not included in GET /rest/events endpoint without a mask specified, but needs to be selected explicitly.

```
{

   "time" : "2017-03-06T23:58:21.844739891+01:00",

   "globalID" : 123,

   "data" : {

      "type" : "file",

      "action" : "deleted",

      "folder": "Dokumente",

      "folderID" : "Dokumente",

      "path" : "testfile",

      "label" : "Dokumente",

      "modifiedBy" : "BPDFDTU"

   },

   "type" : "RemoteChangeDetected",

   "id" : 2
}
```

Deprecated since version v1.1.2: The folderID field is a legacy name kept only for compatibility. Use the folder field with identical content instead.

### RemoteDownloadProgress
This event is emitted when a DownloadProgress message is received. It returns a map data of filenames with a count of downloaded blocks. The files in questions are currently being downloaded on the remote device and belong to folder.

```
{

   "time" : "2017-03-07T00:11:37.65838955+01:00",

   "globalID" : 170,

   "data" : {

      "state" : {

         "tahr64-6.0.5.iso" : 1784

      },

      "device" : "F4HSJVO-CP2C3IL-YLQYLSU-XTYODAG-PPU4LGV-PH3MU4N-G6K56DV-IPN47A",

      "folder" : "Dokumente"

   },

   "type" : "RemoteDownloadProgress",

   "id" : 163
}
```

### RemoteIndexUpdated
Generated each time new index information is received from a device.

```
{

    "id": 44,

    "globalID": 44,

    "type": "RemoteIndexUpdated",

    "time": "2014-07-13T21:04:35.394184435+02:00",

    "data": {

        "device": "NFGKEKE-7Z6RTH7-I3PRZXS-DEJF3UJ-FRWJBFO-VBBTDND-4SGNGVZ-QUQHJAG",

        "folder": "lightroom",

        "items": 1000

    }
}
```

### Starting
Emitted exactly once, when Syncthing starts, before parsing configuration etc.

```
{

    "id": 1,

    "globalID": 1,

    "type": "Starting",

    "time": "2014-07-17T13:13:32.044470055+02:00",

    "data": {

        "home": "/home/jb/.config/syncthing"

    }
}
```

### StartupComplete
Emitted exactly once, when initialization is complete and Syncthing is ready to start exchanging data with other devices.

```
{

    "id": 1,

    "globalID": 1,

    "type": "StartupComplete",

    "time": "2014-07-13T21:03:18.383239179+02:00",

    "data": null
}
```

### StateChanged
Emitted when a folder changes state. Possible states are idle, scanning, syncing and error. The field duration is the number of seconds the folder spent in state from. In the example below, the folder default was in state scanning for 0.198 seconds and is now in state idle.

```
{

    "id": 8,

    "globalID": 8,

    "type": "StateChanged",

    "time": "2014-07-17T13:14:28.697493016+02:00",

    "data": {

        "folder": "default",

        "from": "scanning",

        "duration": 0.19782869900000002,

        "to": "idle"

    }
}
```

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors


syncthing-faq

package: syncthing

title: syncthing-faq(7)

summary: Frequently Asked Questions

text:
# syncthing-faq(7)

## NAME
syncthing-faq - Frequently Asked Questions

•

General

- What is Syncthing?

- Is it “syncthing”, “Syncthing” or “SyncThing”?

- What things are synced?

- Is synchronization fast?

- How does Syncthing differ from BitTorrent/Resilio Sync?

- Is there an iOS client?

- Should I keep my device IDs secret?

•

Troubleshooting

- Where are the Syncthing logs?

- Why is the sync so slow?

- Why does it use so much CPU?

- Why is the setup more complicated than BitTorrent/Resilio Sync?

- Why do I get “Host check error” in the GUI/API?

- My Syncthing database is corrupt

- Why do I see Syncthing twice in task manager?

- How can I view the history of changes?

- Does the audit log contain every change?

- Why does Syncthing connect to this unknown/suspicious address?

- I am seeing the error message “folder marker missing”. What do I do?

- Why do my Windows computers always connect through a relay?

•

Usage

- What if there is a conflict?

- How do I serve a folder from a read only filesystem?

- I really hate the .stfolder directory, can I remove it?

- Am I able to nest shared folders in Syncthing?

- How do I rename/move a synced folder?

- How do I configure multiple users on a single machine?

- Does Syncthing support syncing between folders on the same system?

- When I do have two distinct Syncthing-managed folders on two hosts, how does Syncthing handle moving files between them?

- Can I help initial sync by copying files manually?

- Is Syncthing my ideal backup application?

- How can I exclude files with brackets ([]) in the name?

- How do I access the web GUI from another computer?

- I don’t like the GUI or the theme. Can it be changed?

- How do I upgrade Syncthing?

- Where do I find the latest release?

- How do I run Syncthing as a daemon process on Linux?

- How do I increase the inotify limit to get my filesystem watcher to work?

- How do I reset the GUI password?

## GENERAL

### What is Syncthing?
Syncthing is an application that lets you synchronize your files across multiple devices. This means the creation, modification or deletion of files on one machine will automatically be replicated to your other devices. We believe your data is your data alone and you deserve to choose where it is stored. Therefore Syncthing does not upload your data to the cloud but exchanges your data across your machines as soon as they are online at the same time.

### Is it “syncthing”, “Syncthing” or “SyncThing”?
It’s Syncthing, although the command and source repository is spelled syncthing so it may be referred to in that way as well. It’s definitely not SyncThing, even though the abbreviation st is used in some circumstances and file names.

### What things are synced?
The following things are always synchronized:

- File contents

- File modification times

The following may be synchronized or not, depending:

- File permissions (when supported by file system; on Windows only the read only bit is synchronized)

- Symbolic links (synced, except on Windows, but never followed)

- File or directory owners and groups (when enabled)

- Extended attributes (when enabled)

- POSIX or NFS ACLs (as part of extended attributes)

NOTE:

Note that what can be synced often depends on the operating system, file system, and possibly other factors. For example, even though Syncthing may try to synchronise symbolic links on Android, this will not succeed, as the OS does not support them on the user storage.

The following are not synchronized;

- Directory modification times (not preserved)

- Hard links (followed, not preserved)

- Windows junctions (synced as ordinary directories; require enabling in the configuration on a per-folder basis)

- Resource forks (not preserved)

- Windows ACLs (not preserved)

- Devices, FIFOs, and other specials (ignored)

- Sparse file sparseness (will become sparse, when supported by the OS & filesystem)

- Syncthing internal files and folders (e.g. .stfolder, .stignore, .stversions, temporary files, etc.)

### Is synchronization fast?
Syncthing segments files into pieces, called blocks, to transfer data from one device to another. Therefore, multiple devices can share the synchronization load, in a similar way to the torrent protocol. The more devices you have online, the faster an additional device will receive the data because small blocks will be fetched from all devices in parallel.

Syncthing handles renaming files and updating their metadata in an efficient manner. This means that renaming a file will not cause a retransmission of that file. Additionally, appending data to existing files should be handled efficiently as well.

Temporary files are used to store partial data downloaded from other devices. They are automatically removed whenever a file transfer has been completed or after the configured amount of time which is set in the configuration file (24 hours by default).

### How does Syncthing differ from BitTorrent/Resilio Sync?
The two are different and not related. Syncthing and BitTorrent/Resilio Sync accomplish some of the same things, namely syncing files between two or more computers.

BitTorrent Sync, now called Resilio Sync, is a proprietary peer-to-peer file synchronization tool available for Windows, Mac, Linux, Android, iOS, Windows Phone, Amazon Kindle Fire and BSD. [1] Syncthing is an open source file synchronization tool.

Syncthing uses an open and documented protocol, and likewise the security mechanisms in use are well defined and visible in the source code. Resilio Sync uses an undocumented, closed protocol with unknown security properties.

[1]

https://en.wikipedia.org/wiki/Resilio_Sync

### Is there an iOS client?
There are no plans by the current Syncthing team to officially support iOS in the foreseeable future.

iOS has significant restrictions on background processing that make it very hard to run Syncthing reliably and integrate it into the system.

However, there is an open source app for iOS, incorporating Syncthing, that attempts to work within these limitations. It provides a native UI and features for selective synchronization as well as on-demand access to files. Most Syncthing features are available, but the native UI is simplified compared to the official client. [2]

There is also a commercial packaging of Syncthing. It provides access to all Syncthing functionalities through the original UI. [3]

[2]

https://github.com/pixelspark/sushitrain

[3]

https://www.mobiussync.com

### Should I keep my device IDs secret?
No. The IDs are not sensitive. Given a device ID it’s possible to find the IP address for that device, if global discovery is enabled on it. Knowing the device ID doesn’t help you actually establish a connection to that device or get a list of files, etc.

For a connection to be established, both devices need to know about the other’s device ID. It’s not possible (in practice) to forge a device ID. (To forge a device ID you need to create a TLS certificate with that specific SHA-256 hash. If you can do that, you can spoof any TLS certificate. The world is your oyster!)

SEE ALSO:

Understanding Device IDs

## TROUBLESHOOTING

### Where are the Syncthing logs?
Syncthing logs to stdout by default. On Windows Syncthing by default also creates syncthing.log in Syncthing’s home directory (run syncthing --paths to see where that is). The command line option --logfile can be used to specify a user-defined logfile. If you only have access to a running instance’s GUI, click the Help -> About menu item, then the Paths tab.

If you’re running a process manager like systemd, check there. If you’re using a GUI wrapper integration, it may keep the logs for you.

### Why is the sync so slow?
When troubleshooting a slow sync, there are a number of things to check.

First of all, verify that you are not connected via a relay. In the “Remote Devices” list on the right side of the GUI, double check that the Connection Type does not start with “Relay”.

Here is an example of a device connected via a relay: [image]

If you are connected via a relay, this is because a direct connection could not be established. Double check and follow the suggestions in Firewall Setup to enable direct connections.

Second, if one of the devices is a very low powered machine (a Raspberry Pi, or a phone, or a NAS, or similar) you are likely constrained by the CPU on that device. See the next question for reasons Syncthing likes a faster CPU.

Third, verify that the network connection is OK. Tools such as iperf or just an Internet speed test can be used to verify the performance here.

### Why does it use so much CPU?
1.

When new or changed files are detected, or Syncthing starts for the first time, your files are hashed using SHA-256.

2.

Data that is sent over the network is compressed (optionally) and encrypted (always). When receiving data it must be decrypted and then (if compressed) decompressed.

3.

There is a certain amount of housekeeping that must be done to track the current and available versions of each file in the index database.

4.

By default Syncthing uses periodic scanning every hour when watching for changes or every minute if that’s disabled to detect file changes. This means checking every file’s modification time and comparing it to the database. This can cause spikes of CPU usage for large folders.

Hashing, compression and encryption cost CPU time. Also, using the GUI causes a certain amount of extra CPU usage to calculate the summary data it presents. Note however that once things are in sync CPU usage should be negligible.

To minimize the impact of this, Syncthing attempts to lower the process priority when starting up.

To further limit the amount of CPU used when syncing and scanning, set the environment variable GOMAXPROCS to the maximum number of CPU cores Syncthing should use at any given moment. For example, GOMAXPROCS=2 on a machine with four cores will limit Syncthing to no more than half the system’s CPU power.

### Why is the setup more complicated than BitTorrent/Resilio Sync?
Security over convenience. In Syncthing you have to set up both sides to connect two devices. An attacker can’t do much with a stolen device ID, because you have to add the device on the other side too. You have better control where your files are transferred.

This is an area that we are working to improve in the long term.

### Why do I get “Host check error” in the GUI/API?
Since version 0.14.6 Syncthing does an extra security check when the GUI/API is bound to localhost - namely that the browser is talking to localhost. This protects against most forms of DNS rebinding attack <https://en.wikipedia.org/wiki/DNS_rebinding> against the GUI.

To pass this test, ensure that you are accessing the GUI using an URL that begins with http://localhost, http://127.0.0.1 or http://[::1]. HTTPS is fine too, of course.

If you are using a proxy in front of Syncthing you may need to disable this check, after ensuring that the proxy provides sufficient authentication to protect against unauthorized access. Either:

- Make sure the proxy sets a Host header containing localhost, or

- Set gui.insecureSkipHostcheck in the advanced settings, or

- Bind the GUI/API to a non-localhost listen port.

In all cases, username/password authentication and HTTPS should be used.

### My Syncthing database is corrupt
This is almost always a result of bad RAM, storage device or other hardware. When the index database is found to be corrupt Syncthing cannot operate and will note this in the logs and exit. To overcome this delete the database folder inside Syncthing’s data directory and re-start Syncthing. It will then need to perform a full re-hashing of all shared folders. You should check your system in case the underlying cause is indeed faulty hardware which may put the system at risk of further data loss.

### Why do I see Syncthing twice in task manager?
One process manages the other, to capture logs and manage restarts. This makes it easier to handle upgrades from within Syncthing itself, and also ensures that we get a nice log file to help us narrow down the cause for crashes and other bugs.

### How can I view the history of changes?
The web GUI contains a Recent Changes button under the device list which displays changes since the last (re)start of Syncthing. With the --audit option you can enable a persistent, detailed log of changes and most activities, which contains a JSON-formatted sequence of events in the ~/.local/state/syncthing/audit-_date_-_time_.log file.

### Does the audit log contain every change?
The audit log (and the Recent Changes window) sees the changes that your Syncthing sees. When Syncthing is continuously connected it usually sees every change happening immediately and thus knows which node initiated the change. When topology gets complex or when your node reconnects after some time offline, Syncthing synchronises with its neighbours: It gets the latest synchronised state from the neighbour, which is the result of all the changes between the last known state (before disconnect or network delay) and the current state at the neighbour, and if there were updates, deletes, creates, conflicts, which were overlapping we only see the latest change for a given file or directory (and the node where that latest change occurred). When we connect to multiple neighbours Syncthing decides which neighbour has the latest state, or if the states conflict it initiates the conflict resolution procedure, which in the end results in a consistent up-to-date state with all the neighbours.

### Why does Syncthing connect to this unknown/suspicious address?
If you see outgoing connections to odd and unexpected addresses these are most likely connections to relay servers. Relay servers are run by volunteers all over the world. They usually listen on ports 443 or 22067, though this is controlled by the user running it. You can compare the address you are concerned about with the current list of active relays <https://relays.syncthing.net>. Relays do not and can not see the data transmitted via them.

### I am seeing the error message “folder marker missing”. What do I do?
Syncthing uses a specific marker usually called .stfolder to determine whether a folder is healthy. This is a safety check to ensure that your folder is properly readable and present on disk. For example, if you remove a USB drive from your computer or unmount a filesystem, then syncthing must know whether you have really deleted all of your files. Therefore, syncthing always checks that the .stfolder is present.

When this error appears, syncthing assumes that the folder has encountered some type of error and will stop syncing it until the .stfolder reappears. Once that happens, all changes made to the folder locally will be synced (i.e. missing files will be considered deletions).

- If you get this error message, check the folder in question on your storage. If you have unmounted the folder (or a parent of it), you must remount it for syncthing to resume syncing this folder.

- If you have moved the folder, you must either move it back to its original location, or remove the folder from within the syncthing UI and re-add it at its new location.

- If the folder is present on disk, with all of its children files and directories, but the .stfolder is still missing: It is possible that a file cleaning software has removed the .stfolder. Some software removes empty folders, and the .stfolder is often empty. This happens particularly often on Android. To remediate, recreate the .stfolder and add a dummy file in it, or add an exception to your cleaning software.

If you are still unsure what has happened, you can remove the folder from within the syncthing UI and re-add it at the same location. This causes syncthing to attempt an automatic re-creation of the .stfolder. Next, it will also reset the database state of this folder. It will be considered a “new” folder, meaning that its files will be merged with files from remote devices.

Also see the marker FAQ for more information about the folder marker.

### Why do my Windows computers always connect through a relay?
When connecting to a new network, Windows by default sets its profile to “Public”. While being more secure, this setting commonly prevents applications like Syncthing from being able to establish direct connections with the device in question, forcing it to connect through a relay. If you would rather connect your devices directly, please follow the official Microsoft instructions on how to change the network profile to “Private” <https://support.microsoft.com/windows/essential-network-settings-and-tasks-in-windows-f21a9bbc-c582-55cd-35e0-73431160a1b9#bkmk_network_profile>.

## USAGE

### What if there is a conflict?
SEE ALSO:

Conflicting Changes

### How do I serve a folder from a read only filesystem?
Syncthing requires a “folder marker” to indicate that the folder is present and healthy. By default this is a directory called .stfolder that is created by Syncthing when the folder is added. If this folder can’t be created (you are serving files from a CD or something) you can instead set the advanced config Marker Name to the name of some file or folder that you know will always exist in the folder.

### I really hate the .stfolder directory, can I remove it?
See the previous question.

### Am I able to nest shared folders in Syncthing?
Sharing a folder that is within an already shared folder is possible, but it has its caveats. What you must absolutely avoid are circular shares. This is just one example, there may be other undesired effects. Nesting shared folders is not supported, recommended or coded for, but it can be done successfully when you know what you’re doing - you have been warned.

### How do I rename/move a synced folder?
Syncthing doesn’t have a direct way to do this, as it’s potentially dangerous to do so if you’re not careful - it may result in data loss if something goes wrong during the move and is synchronized to your other devices.

The easy way to rename or move a synced folder on the local system is to remove the folder in the Syncthing UI, move it on disk, then re-add it using the new path.

It’s important to do this when the folder is already in sync between your devices, as it is otherwise unpredictable which changes will “win” after the move. Changes made on other devices may be overwritten, or changes made locally may be overwritten by those on other devices.

An alternative way is to shut down Syncthing, move the folder on disk (including the .stfolder marker), edit the path directly in config.xml in the configuration folder (see Syncthing Configuration) and then start Syncthing again.

### How do I configure multiple users on a single machine?
Each user should run their own Syncthing instance. Be aware that you might need to configure listening ports such that they do not overlap (see Syncthing Configuration).

### Does Syncthing support syncing between folders on the same system?
No. Syncthing is not designed to sync locally and the overhead involved in doing so using Syncthing’s method would be wasteful. There are better programs to achieve this such as rsync <https://rsync.samba.org/> or Unison <https://www.cis.upenn.edu/~bcpierce/unison>.

### When I do have two distinct Syncthing-managed folders on two hosts, how does Syncthing handle moving files between them?
Syncthing does not specially handle this case, and most files will most likely get re-downloaded.

In detail, the behavior depends on the scan order. If you have folders A and B, and move files from A to B, if A gets scanned first, it will announce the removal of the files to others who will then remove the files. As you rescan B, B will announce the addition of new files, and other peers will have nowhere to get them from apart from re-downloading them.

If B gets rescanned first, B will announce additions first, and remote peers will then reconstruct the files (not rename, more like copying block by block) from A, and then as A gets rescanned, it will remove the files from A.

A workaround would be to copy first from A to B, rescan B, wait for B to copy the files on the remote side, and then delete from A.

### Can I help initial sync by copying files manually?
If you have a large folder that you want to keep in sync over a not-so-fast network, and you have the possibility to move all files to the remote device in a faster manner, here is a procedure to follow:

- Create the folder on the local device, but don’t share it with the remote device yet.

- Copy the files from the local device to the remote device using regular file copy. If this takes a long time (perhaps requiring travelling there physically), it may be a good idea to make sure that the files on the local device are not updated while you are doing this.

- Create the folder on the remote device, and copy the Folder ID from the folder on the local device, as we want the folders to be considered the same. Then wait until scanning the folder is done.

- Now share the folder with the other device, on both sides. Syncthing will exchange file information, updating the database, but existing files will not be transferred. This may still take a while initially, be patient and wait until it settled.

### Is Syncthing my ideal backup application?
No. Syncthing is not a great backup application because all changes to your files (modifications, deletions, etc.) will be propagated to all your devices. You can enable versioning, but we encourage you to use other tools to keep your data safe from your (or our) mistakes.

### How can I exclude files with brackets ([]) in the name?
The patterns in .stignore are glob patterns, where brackets are used to denote character ranges. That is, the pattern q[abc]x will match the files qax, qbx and qcx.

To match an actual file called q[abc]x the pattern needs to “escape” the brackets, like so: q\[abc\]x.

On Windows, use the | character to escape the brackets (q|[abc|]x), as the \ character is used as a path separator.

### How do I access the web GUI from another computer?
The default listening address is 127.0.0.1:8384, so you can only access the GUI from the same machine. This is for security reasons. To access it from another computer, change the GUI listen address option in the web GUI from 127.0.0.1:8384 to 0.0.0.0:8384, or change the config.xml:

```
<gui enabled="true" tls="false">

  <address>127.0.0.1:8384</address>
```

to

```
<gui enabled="true" tls="true">

  <address>0.0.0.0:8384</address>
```

Then the GUI is accessible from everywhere. There is no filtering based on e.g. source address (use a firewall for that). You should set a password and enable HTTPS with this configuration. You can do this from inside the GUI.

If both your computers are Unix-like (Linux, Mac, etc.) you can also leave the GUI settings at default and use an SSH port forward to access it. For example,

```
$ ssh -L 9090:127.0.0.1:8384 user@othercomputer.example.com
```

will log you into othercomputer.example.com, and present the remote Syncthing GUI on http://localhost:9090 on your local computer.

If you only want to access the remote GUI and don’t want the terminal session, use this example:

```
$ ssh -N -L 9090:127.0.0.1:8384 user@othercomputer.example.com
```

If only your remote computer is Unix-like, you can still access it with SSH from Windows. Under Windows 10 or later you can use the same ssh command if you install the OpenSSH Client <https://learn.microsoft.com/windows-server/administration/openssh/openssh_install_firstuse>.

### I don’t like the GUI or the theme. Can it be changed?
You can change the theme in the settings. Syncthing ships with other themes than the default.

If you want a custom theme or a completely different GUI, you can add your own. By default, Syncthing will look for a directory gui inside the Syncthing home folder. To change the directory to look for themes, you need to set the STGUIASSETS environment variable. To get the concrete directory, run syncthing with the --paths parameter. It will print all the relevant paths, including the “GUI override directory”.

To add e.g. a red theme, you can create the file red/assets/css/theme.css inside the GUI override directory to override the default CSS styles.

To create a whole new GUI, you should checkout the files at https://github.com/syncthing/syncthing/tree/main/gui/default to get an idea how to do that.

### How do I upgrade Syncthing?
If you use a package manager such as Debian’s apt-get, you should upgrade using the package manager. If you use the binary packages linked from Syncthing.net, you can use Syncthing’s built-in automatic upgrade functionality.

- If automatic upgrades is enabled (which is the default), Syncthing will upgrade itself automatically within 24 hours of a new release.

- The upgrade button appears in the web GUI when a new version has been released. Pressing it will perform an upgrade.

- To force an upgrade from the command line, run syncthing --upgrade.

Note that your system should have CA certificates installed which allows a secure connection to GitHub (e.g. FreeBSD requires sudo pkg install ca_root_nss). If curl or wget works with normal HTTPS sites, then so should Syncthing.

### Where do I find the latest release?
We release new versions through GitHub. The latest release is always found on the release page <https://github.com/syncthing/syncthing/releases/latest>. Unfortunately GitHub does not provide a single URL to automatically download the latest version. We suggest to use the GitHub API <https://api.github.com/repos/syncthing/syncthing/releases/latest> and parsing the JSON response.

### How do I run Syncthing as a daemon process on Linux?
If you’re using systemd, runit, or upstart, we ship example configurations <https://github.com/syncthing/syncthing/tree/main/etc>.

If however you’re not using one of these tools, you have a couple of options. If your system has a tool called start-stop-daemon installed (that’s the name of the command, not the package), look into the local documentation for that, it will almost certainly cover 100% of what you want to do. If you don’t have start-stop-daemon, there are a bunch of other software packages you could use to do this. The most well known is called daemontools, and can be found in the standard package repositories for almost every modern Linux distribution. Other popular tools with similar functionality include S6 and the aforementioned runit.

### How do I increase the inotify limit to get my filesystem watcher to work?
You are probably reading this because you encountered the following error with the filesystem watcher on linux:

Failed to start filesystem watcher for folder yourLabel (yourID): failed to set up inotify handler. Please increase inotify limits, see https://docs.syncthing.net/users/faq.html#inotify-limits

Linux typically restricts the number of watches per user (usually 8192). If you have many directories, you will need to adjust that number.

On many Linux distributions you can run the following to fix it:

```
echo "fs.inotify.max_user_watches=204800" | sudo tee -a /etc/sysctl.conf
```

On Arch Linux and potentially others it is preferred to write this line into a separate file, i.e. you should run:

```
echo "fs.inotify.max_user_watches=204800" | sudo tee -a /etc/sysctl.d/90-inotify-max-user-watches.conf
```

This only takes effect after a reboot. To adjust the limit immediately, run:

```
echo 204800 | sudo tee /proc/sys/fs/inotify/max_user_watches
```

### How do I reset the GUI password?
If you’ve forgotten / lost the GUI password, you can reset it using the --gui-password (and possibly --gui-user) options to the syncthing generate subcommand. This should be done while Syncthing is not running.

1.

Stop Syncthing: syncthing cli operations shutdown

2.

syncthing generate --gui-password=myNewPassword --gui-user=newUserName

3.

Restart Syncthing as usual.

Alternatively, in step 2, you can manually delete the <user> and <password> XML tags from the <gui> block in file config.xml. The location of the file depends on the OS and is described in the configuration documentation.

For example, the two emphasized lines below would be removed from the file.

```
<gui enabled="true" tls="false">

   <address>127.0.0.1:8384</address>

   <user>syncguy</user>

   <password>$2a$10$s9wWHOQe...Cq7GPye69</password>

   <apikey>9RCKohqCAyrj5RjpyZdR2wXmQ9PyQFeN</apikey>

   <theme>default</theme>
</gui>
```

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors

branch: sisyphus


syncthing-globaldisco

title: syncthing-globaldisco(7)

summary: Global Discovery Protocol v3

text:
# syncthing-globaldisco(7)

## NAME
syncthing-globaldisco - Global Discovery Protocol v3

## ANNOUNCEMENTS
A device should announce itself at startup. It does this by an HTTPS POST to the announce server URL. Standard discovery currently requires the path to be “/v2/”, yet this can be up to the discovery server. The POST has a JSON payload listing connection addresses (if any):

```
{

        addresses: ["tcp://192.0.2.45:22000", "tcp://:22202", "relay://192.0.2.99:22028"],
}
```

It’s OK for the “addresses” field to be either the empty list ([]), null, or missing entirely. An announcement with the field missing or empty is however not useful…

Any empty or unspecified IP addresses (i.e. addresses like tcp://:22000, tcp://0.0.0.0:22000, tcp://[::]:22000) are interpreted as referring to the source IP address of the announcement.

The device ID of the announcing device is not part of the announcement. Instead, the server requires that the client perform certificate authentication. The device ID is deduced from the presented certificate.

The server response is empty, with code 204 (No Content) on success. If no certificate was presented, status 403 (Forbidden) is returned. If the posted data doesn’t conform to the expected format, 400 (Bad Request) is returned.

In successful responses, the server may return a Reannounce-After header containing the number of seconds after which the client should perform a new announcement.

In error responses, the server may return a Retry-After header containing the number of seconds after which the client should retry.

Performing announcements significantly more often than indicated by the Reannounce-After or Retry-After headers may result in the client being throttled. In such cases the server may respond with status code 429 (Too Many Requests).

## QUERIES
Queries are performed as HTTPS GET requests to the announce server URL. The requested device ID is passed as the query parameter “device”, in canonical string form, i.e. https://discovery.syncthing.net/?device=ABC12345-....

Successful responses will have status code 200 (OK) and carry a JSON payload of the same format as the announcement above. The response will not contain empty or unspecified addresses.

If the “device” query parameter is missing or malformed, the status code 400 (Bad Request) is returned.

If the device ID is of a valid format but not found in the registry, 404 (Not Found) is returned.

If the client has exceeded a rate limit, the server may respond with 429 (Too Many Requests).

## AUTHENTICATION
Global discovery is spoken over HTTPS and is protected against attackers in the same manner as other HTTPS traffic. However, there are a few Syncthing specific considerations on top of this. As mentioned above, for announcements the client must provide a certificate to prove ownership of the announced device ID.

In addition, Syncthing has a mechanism to verify the identity of the discovery server. While this would normally be accomplished by using a CA signed certificate, Syncthing often runs in environments with outdated or simply nonexistent root CA bundles. Instead, Syncthing can verify the discovery server certificate fingerprint using the device ID mechanism. This is certificate pinning and conveyed in the Syncthing configuration as a synthetic “id” parameter on the discovery server URL: https://discovery.syncthing.net/?id=.... The “id” parameter is not, in fact, sent to the discovery server - it’s used by Syncthing itself to know which certificate to expect on the server side.

The public discovery network uses this authentication mechanism instead of CA signed certificates.

The discovery server prints its certificate ID in this manner on startup.

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors


syncthing-localdisco

title: syncthing-localdisco(7)

summary: Local Discovery Protocol v4

text:
# syncthing-localdisco(7)

## NAME
syncthing-localdisco - Local Discovery Protocol v4

## MODE OF OPERATION
Each participating device periodically sends an Announcement packet. It also keeps a table of the announcements it has seen. There is no way to solicit a reply; the only message type is Announcement.

On multihomed hosts the announcement packets should be sent on each interface on which Syncthing will accept connections.

The announcement packet is sent over UDP.

For IPv4, the Announcement packet is broadcast either to the link-specific broadcast address, or to the generic link-local broadcast address 255.255.255.255, with destination port 21027.

For IPv6, the Announcement packet is multicast to the transient link-local multicast address ff12::8384, with destination port 21027.

It is recommended that local discovery Announcement packets be sent on a 30 to 60 second interval, possibly with immediate transmissions when a previously unknown device is discovered or a device has restarted (see the instance_id field).

## DEVICE ID
The device ID is the SHA-256 (32 bytes) of the device X.509 certificate. See Understanding Device IDs in the Syncthing documentation.

## ANNOUNCEMENT PACKET
The Announcement packet has the following structure:

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Magic                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                       Announce Message                        \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```

There is no explicit length field as the length is given by the length of the discovery announcement packet itself.

The Magic field is a 32 bit word representing 0x2EA7D90B in network (big endian) byte order. It identifies the packet as being a Syncthing discovery protocol packet.

The Announce Message contents are in protocol buffer format using the following schema:

```
message Announce {

    bytes           id          = 1;

    repeated string addresses   = 2;

    int64           instance_id = 3;
}
```

The id field contains the Device ID of the sending device.

The addresses field contains a list of addresses where the device can be contacted. Direct connections will typically have the tcp:// scheme. Relay connections will typically use the relay:// scheme.

When interpreting addresses with an unspecified address, e.g., tcp://0.0.0.0:22000 or tcp://:42424, the source address of the discovery announcement is to be used.

The instance_id field is set to a randomly generated ID at client startup. Other devices on the network can detect a change in instance ID between two announces and conclude that the announcing device has restarted.

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors


syncthing-networking

title: syncthing-networking(7)

summary: Firewall Setup

text:
# syncthing-networking(7)

## NAME
syncthing-networking - Firewall Setup

## ROUTER SETUP

### Port Forwards
If you have a NAT router which supports UPnP, the easiest way to get a working port forward is to make sure UPnP setting is enabled on both Syncthing and the router – Syncthing will try to handle the rest. If it succeeds you will see a message in the console saying:

```
Created UPnP port mapping for external port XXXXX on UPnP device YYYYY.
```

If this is not possible or desirable, you should set up a port forwarding for ports 22000/TCP and 22000/UDP (or whichever port is set in the Sync Protocol Listen Address setting). The external forwarded ports and the internal destination ports have to be the same (e.g. 22000/TCP).

Communication in Syncthing works both ways. Therefore if you set up port forwards for one device, other devices will be able to connect to it even when they are behind a NAT network or firewall.

In the absence of port forwarding, Relaying may work well enough to get devices connected and synced, but will perform poorly in comparison to a direct connection.

### Local Discovery
The router needs to allow/forward broad-/multicasts for local discovery to work. Usually these are allowed by default in a single local subnet, but may be blocked between different subnets or even between a bridged Wi-Fi and LAN.

If you are unable to set up your router thus or your firewall as shown below, and your devices have static IP addresses, you can specify them directly by changing the default dynamic setting for Addresses to something like: tcp://192.168.1.xxx:22000, dynamic.

## LOCAL FIREWALL
If your PC has a local firewall, you will need to open the following ports for incoming and outgoing traffic:

- Port 22000/TCP: TCP based sync protocol traffic

- Port 22000/UDP: QUIC based sync protocol traffic

- Port 21027/UDP: for discovery broadcasts on IPv4 and multicasts on IPv6

If you configured a custom port in the Sync Protocol Listen Address setting, you have to adapt the firewall rules accordingly.

### Uncomplicated Firewall (ufw)
If you’re using ufw on Linux and have installed the Syncthing package <https://apt.syncthing.net/>, you can allow the necessary ports by running:

```
sudo ufw allow syncthing
```

If you also want to allow external access to the Syncthing web GUI, run:

```
sudo ufw allow syncthing-gui
```

Allowing external access is not necessary for a typical installation.

You can then verify that the ports mentioned above are allowed:

```
sudo ufw status verbose
```

In case you installed Syncthing manually you can follow the instructions to manually add the syncthing preset <https://github.com/syncthing/syncthing/tree/main/etc/firewall-ufw> to ufw.

### Firewalld
If you are using Firewalld <https://firewalld.org/> it has included support for syncthing (since version 0.5.0, January 2018), and you can enable it with:

```
sudo firewall-cmd --zone=public --add-service=syncthing --permanent
sudo firewall-cmd --reload
```

Similarly there is also a syncthing-gui service.

## REMOTE WEB GUI
To be able to access the web GUI from other computers, you need to change the GUI Listen Address setting from the default 127.0.0.1:8384 to 0.0.0.0:8384. You also need to open the port in your local firewall if you have one.

### Tunneling via SSH
If you have SSH access to the machine running Syncthing but would rather not open the web GUI port to the outside world, you can access it through a SSH tunnel instead. You can start a tunnel with a command like the following:

```
ssh -L 9999:localhost:8384 machine
```

This will bind to your local port 9999 and forward all connections from there to port 8384 on the target machine. This still works even if Syncthing is bound to listen on localhost only.

## VIA A PROXY
Syncthing can use a SOCKS5 proxy for outbound connections. Please see Using Proxies.

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors


syncthing-relay

title: syncthing-relay(7)

summary: Relay Protocol v1

text:
# syncthing-relay(7)

## NAME
syncthing-relay - Relay Protocol v1

## WHAT IS A RELAY?
Relay is a service which relays data between two devices which are not able to connect to each other directly otherwise. This is usually due to both devices being behind a NAT and neither side being able to open a port which would be directly accessible from the internet.

A relay was designed to relay BEP protocol, hence the reliance on device ID’s in the protocol spec, but at the same time it is general enough that could be reused by other protocols or applications, as the data transferred between two devices which use a relay is completely obscure and does not affect the relaying.

## OPERATION MODES
Relay listens on a single TCP socket, but has two different connection modes, where a connection mode is a predefined set of messages which the relay and the device are expecting to exchange.

The first mode is the protocol mode which allows a client to interact with the relay, for example join the relay, or request to connect to a device, given it is available on the relay. Similarly to BEP, protocol mode requires the device to connect via TLS using a strong suite of ciphers (same as BEP), which allows the relay to verify and derive the identity (Device ID) of the device.

The second mode is the session mode which after a few initial messages connects two devices directly to each other via the relay, and is a plain-text protocol, which for every byte written by one device, sends the same set of bytes to the other device and vica versa.

## IDENTIFYING THE CONNECTION MODE
Because both connection modes operate over the same single socket, a method of detecting the connection mode is required.

When a new client connects to the relay, the relay checks the first byte that the client has sent, and if that matches 0x16, that implies to us that the connection is a protocol mode connection, due to 0x16 being the first byte in the TLS handshake, and only protocol mode connections use TLS.

If the first byte is not 0x16, then we assume that the connection is a session mode connection.

## PROTOCOL MODE
Protocol mode uses TLS and protocol name defined by the TLS header should be bep-relay.

Protocol mode has two submodes: 1. Permanent protocol submode - Joining the relay, and waiting for messages from the relay asking to connect to some device which is interested in having a session with you. 2. Temporary protocol submode - Only used to request a session with a device which is connected to the relay using the permanent protocol submode.

### Permanent protocol submode
A permanent protocol submode begins with the client sending a JoinRelayRequest message, which the relay responds to with either a ResponseSuccess or ResponseAlreadyConnected message if a client with the same device ID already exists.

After the client has joined, no more messages are exchanged apart from Ping/Pong messages for general connection keep alive checking.

From this point onwards, the client stand-by’s and waits for SessionInvitation messages from the relay, which implies that some other device is trying to connect with you. SessionInvitation message contains the unique session key which then can be used to establish a connection in session mode.

If the client fails to send a JoinSessionRequest message within the first ping interval, the connection is terminated. If the client fails to send a message (even if it’s a ping message) every minute (by default), the connection is terminated.

### Temporary protocol submode
A temporary protocol submode begins with ConnectRequest message, to which the relay responds with ResponseNotFound if the device the client it is after is not available, with a RelayFull if the relay has reached its limits, or with a SessionInvitation, which contains the unique session key which then can be used to establish a connection in session mode.

The connection is terminated immediately after that.

### Example Exchange
Client A - Permanent protocol submode Client B - Temporary protocol submode

\#

Client (A)

Relay

Client (B)

1

JoinRelayRequest->

2

<-ResponseSuccess

3

Ping->

4

<-Pong

5

<-ConnectRequest(A)

6

SessionInvitation(A)->

7

<-SessionInvitation(B)

8

(Disconnects)

9

Ping->

10

<-Pong

11

Ping->

12

<-Pong

## SESSION MODE
The first and only message the client sends in the session mode is the JoinSessionRequest message which contains the session key identifying which session you are trying to join. The relay responds with one of the following messages:

1.

ResponseNotFound - Session key is invalid

2.

ResponseAlreadyConnected - Session is full (both sides already connected)

3.

ResponseSuccess - You have successfully joined the session

4.

RelayFull - Relay limits are too strict for you to be able to join the session. The relay immediately terminates the connection after sending this.

After the successful response, all the bytes written and received will be relayed between the two devices in the session directly.

### Example Exchange
Client A is the first to join the session.

Client B is the second to join the session.

Both are in session mode.

\#

Client (A)

Relay

Client (B)

1

JoinSessionRequest(A)->

2

<-ResponseSuccess

3

Data->

(Buffers data)

4

Data->

(Buffers data)

5

<-JoinSessionRequest(B)

6

ResponseSuccess->

7

Relays data ->

8

Relays data ->

9

<-Relays data

<-Data

## MESSAGES
All messages are preceded by a header message. Header message contains the magic value 0x9E79BC40, message type integer, and message length.

WARNING:

Some messages have no content, apart from the implied header which allows us to identify what type of message it is.

### Header structure

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Magic                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Message Type                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Message Length                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct Header {

        unsigned int Magic;

        int MessageType;

        int MessageLength;
}
```

### Ping message (Type = 0)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct Ping {
}
```

### Pong message (Type = 1)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct Pong {
}
```

### JoinRelayRequest message (Type = 2)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct JoinRelayRequest {
}
```

### JoinSessionRequest message (Type = 3)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Length of Key                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                     Key (variable length)                     \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct JoinSessionRequest {

        opaque Key<32>;
}
```

: Key

This is a unique random session key generated by the relay server. It is used to identify which session you are trying to connect to.

### Response message (Type = 4)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Code                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Length of Message                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                   Message (variable length)                   \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct Response {

        int Code;

        string Message<>;
}
```

: Code

An integer representing the status code.

: Message

Message associated with the code.

```
ResponseSuccess           = Response{0, "success"}
ResponseNotFound          = Response{1, "not found"}
ResponseAlreadyConnected  = Response{2, "already connected"}
ResponseInternalError     = Response{99, "internal error"}
ResponseUnexpectedMessage = Response{100, "unexpected message"}
```

### ConnectRequest message (Type = 5)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Length of ID                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                     ID (variable length)                      \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct ConnectRequest {

        opaque ID<32>;
}
```

: ID

Device ID to which the client would like to connect.

### SessionInvitation message (Type = 6)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Length of From                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                    From (variable length)                     \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Length of Key                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                     Key (variable length)                     \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Length of Address                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                   Address (variable length)                   \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            0x0000             |             Port              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Server Socket (V=0 or 1)                   |V|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct SessionInvitation {

        opaque From<32>;

        opaque Key<32>;

        opaque Address<32>;

        unsigned int Port;

        bool ServerSocket;
}
```

: From

Device ID identifying who you will be connecting with.

: Key

A unique random session key generated by the relay server. It is used to identify which session you are trying to connect to.

: Address

An optional IP address on which the relay server is expecting you to connect, in order to start a connection in session mode. Empty/all zero IP should be replaced with the relay’s public IP address that was used when establishing the protocol mode connection.

: Port

The port on which the relay server is expecting you to connect, in order to start a connection in session mode.

: Server Socket

Because both sides connecting to the relay use the client side of the socket, and some protocols behave differently depending if the connection starts on the server side or the client side, this boolean indicates which side of the connection this client should assume it’s getting. The value is inverted in the invitation which is sent to the other device, so that there is always one client socket, and one server socket.

### RelayFull message (Type = 7)

```
 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
struct RelayFull {
}
```

## HOW SYNCTHING USES RELAYS, AND GENERAL SECURITY
In the case of Syncthing and BEP, when two devices connect via relay, they start their standard TLS connection encapsulated within the relay’s plain-text session connection, effectively upgrading the plain-text connection to a TLS connection.

Even though the relay could be used for man-in-the-middle attack, using TLS at the application/BEP level ensures that all the traffic is safely encrypted, and is completely meaningless to the relay. Furthermore, the secure suite of ciphers used by BEP provides forward secrecy, meaning that even if the relay did capture all the traffic, and even if the attacker did get their hands on the device keys, they would still not be able to recover/decrypt any traffic which was transported via the relay.

After establishing a relay session, Syncthing looks at the SessionInvitation message, and depending which side it has received, wraps the raw socket in either a TLS client socket or a TLS server socket depending on the ServerSocket boolean value in the SessionInvitation, and starts the TLS handshake.

From that point onwards it functions exactly the same way as if Syncthing was establishing a direct connection with the other device over the internet, performing device ID validation, and full TLS encryption, and provides the same security properties as it would provide when connecting over the internet.

## EXAMPLES OF STRONG CIPHER SUITES
ID

Name

Description

0x009F

DHE-RSA-AES256-GCM-SHA384

TLSv1.2 DH RSA AESGCM(256) AEAD

0x006B

DHE-RSA-AES256-SHA256

TLSv1.2 DH RSA AES(256) SHA256

0xC030

ECDHE-RSA-AES256-GCM-SHA384

TLSv1.2 ECDH RSA AESGCM(256) AEAD

0xC028

ECDHE-RSA-AES256-SHA384

TLSv1.2 ECDH RSA AES(256) SHA384

0x009E

DHE-RSA-AES128-GCM-SHA256

TLSv1.2 DH RSA AESGCM(128) AEAD

0x0067

DHE-RSA-AES128-SHA256

TLSv1.2 DH RSA AES(128) SHA256

0xC02F

ECDHE-RSA-AES128-GCM-SHA256

TLSv1.2 ECDH RSA AESGCM(128) AEAD

0xC027

ECDHE-RSA-AES128-SHA256

TLSv1.2 ECDH RSA AES(128) SHA256

## AUTHOR
The Syncthing Authors

## COPYRIGHT
2014-2026, The Syncthing Authors